I got a call one time about the same thing. Only luke warm water to the home, and the gas flames were in an uproar.
As I got out of my van and walked down the driveway, I could hear water running. The sound was like a river in a forest. When I got my first look at the water heater, I could see water rushing out of the pan and down the drain. It was a full fledged tank rupture and a good thing there was a pan to catch and drain all the water. Without the drain pan the carpets in the first floor would have been soaked.
I've also had something similar with a pipe leak where the water heater wasn't keeping up. One was a leak below ground. You could see the water meter spinning, but no sign of water anywhere. It must have been making it's way below ground to Puget Sound.